In order to study the dynamic change trend of community structure and the status of the fishery resources in Yueqing Bay mouth, the species composition, species number, diversity of fish communities was studied.A total of 49 species were identified, which belonged to 39 genera in 26 families of 10 orders, and species number in autumn is higher than spring.The species numbers in spring were less than that in autumn especially in Oujiang estuary, and the general spatial distribution trend of fish species in autumn was from east to west.The diversity in weight of the species in spring was lower than that in the autumn, while the individual diversity wass higher than that in autumn.There was obvious correlation between species number and diversity indexes.The study showed that fishes species types mainly belonged to inshore estuary species and most of them were eurythermic and oligohalabous species in Yueqing Bay mouth, because this area was adjacent to Oujiang estuary which has much runoff volume.Due to the effect of geographical position and hydrological environment, there were more warm-water species The characteristic of the general plane distribution was that the species is more rich in autumn than that spring, which was affected by the freshwater masses in spring , and Taiwan warm current confronted with Zhejiang coastal current in autumn.The cause of difference of fish community diversity in between spring and autumn mainly was that the fish size and quantity changed with seasons.%为研究乐清湾口海域鱼类群落结构动态变化趋势和渔业资源现状，对该海域鱼类物种组成、种类数、多样性等群落结构特征进行调查分析。共鉴定出鱼类49种，隶属于10目26科39属。结果显示，春季物种数较秋季少，春季在瓯江口水域物种明显较少，秋季物种数空间分布大致为东西走向；春季种类重量多样性低于秋季，但尾数多样性高于秋季，鱼类种类数与多样性指数之间有较强的相关性。研究表明，乐清湾口海域的鱼类种类类型以近岸河口性鱼类为主，且大多为广温、广盐性种类；该海域位于河口，受瓯江径流影响较大；受地理位置和水文环境影响，该海域暖水性种类较多；种类数平面分布特征主要是春季受瓯江径流淡水水团影响，而秋季受交汇水团影响，物种丰富；两季鱼类多样性不同，是因为鱼类个体大小、数量随着季节的变化而变化。
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